Abstract: CoSnS₂ thin films were prepared by two methods. In the so-called two-step electrode-position method, SnS thin film was first electrodeposited, and then CoS thin film was prepared on it, at last, thermal annealing of this double layer specimen was performed in order to obtain CoSnS₂ thin film of 1250nm. In the so-called three-element co-electrodeposition method, complexing agent of EDTA was added in order to adjust the electrodeposition potential of Co, Sn and S, so that they could co-electrodeposit and form CoSnS₂ thin film of 620nm. The mechanism of the two methods was explored, and the influence of preparation conditions on the structural and optical properties of the films was studied. All the as-deposited films are of polycrystalline γ-Co₆S₅ with cubic structure and SnS with orthor-hombic structure. The direct optical band gap of 1.05～ 1.25 eV and the indirect optical band gap of 0.11～ 0.71 eV are observed, which can be modified by the preparation parameters.